Insulating a casing and tubing string in an oil well for a hot fluid drive



H. W. PARKER INSULATING A CASING AND TUBING STRING IN AN OIL WELL FOR 'AHOT FLUID DRIVE Filed June 12, 1967 A TTORNEVS United States Patent3,451,479 INSULATING A CASING AND TUBING STRING IN AN OIL WELL FOR A HOTFLUID DRIVE Harry W. Parker, Bartlesville, Okla., assignor to PhillipsPetroleum Company, a corporation of Delaware Filed June 12, 1967, Ser.No. 645,442 Int. Cl. E21b 21/00, 43/24, 33/03 US. Cl. 166303 4 ClaimsABSTRACT OF THE DISCLOSURE Tubing and casing strings in a wellpenetrating an oil stratum to be produced by hot fluid drive, such aswith steam, are coated on the walls thereof forming the annulus bypacking off the annulus adjacent or near the stratum, filling theannulus with an aqueous solution of a water-soluble inorganic salt, suchas borax, sodium carbonate, sodium sulfate, and mixtures thereof,preferably containing a binder, and injecting a hot fluid thru thetubing string into the stratum to evaporate water from the solution inthe annulus while venting steam therefrom at the wellhead and deposit asubstantial coat of the salt in solid form on the walls of the annulus.

This invention relates to a method for insulating the walls of a casingand tubing string forming the annulus of a well penetrating an oilstratum to be used in a hot fluid drive process and to the resultinginsulated tubing and casing strings.

The production of oil from underground oil-bearing strata by hot fluiddrive such as steam, hot water, and in situ combustion is conventionalin the petroleum industry. In hot steam drive at temperatures above 400F. and as high as 750 F., the casing is subjected to these extremetemperatures, resulting in casing buckling and severe damage to thecement around the casing. Similar deterioration and damage to the casingoften results from reverse burning in situ combustion wherein the hotgases from the combustion zone pass thru hot sand or rock in passing tothe production well and are at temperatures up to 1000 F. and higher. Inaddition to the damage to the downhole casing, there is also asubstantial and expensive heat loss to the strata surrounding the casinggenerally termed the overburden. Slip-on and wrap-on insulation ofvarious types have been proposed and it is estimated that suchinsulation will reduce thermal losses by more than eighty percent andprovide adequate protection for the downhole casing.

This invention is concerned with a method of insulating the walls of thecasing and tubing strings forming the annulus of a well which is simple,practical, and economically feasible and with the resulting insulatedtubing and casing strings.

Accordingly, it is an object of the invention to provide a simple andeffective method for insulating the inner wall of a casing string andthe outer wall of a tubing string forming the annulus of a well, whilethe strings are in place in the well. Other objects of the inventionwill become apparent to one skilled in the art upon consideration of theaccompanying disclosure.

A broad aspect of the invention comprises setting a packer downhole on atubing string in a well leading to a stratum containing oil to seal offthe annulus between the tubing string and the surrounding casing,substantially filling the annulus above the packer with a concentratedaqueous solution of a water-soluble inorganic salt, injecting a hotfluid thru the tubing string into the stratum so as to heat and boilsaid solution while venting steam from the annulus at the wellhead, andcontinuing the injection of hot fluid thru the tubing string so as todeposit 3,451,479 Patented June 24, 1969 said salt in solid form on theoutside wall of the tubing string and the inside wall of the casingstring substantially to the packer. The salt solution can be saturatedand contain undissolved salt. The salt solution may also contain asuitable binder for binding the particles of salt together and forbinding the salt to the walls of the tubing and casing strings. One ormore salts of the group borax, sodium carbonate, and sodium sulfate aregenerally utilized. Concentrated solutions of these salts are effectivein forming porous insulating coatings on the strings. Sodium silicateand metal stearate soaps provide suitable binders for the salt particlesand for binding the salt particles to the metal in the well. It is alsofeasible to incorporate in the salt solution solid polymers inparticulate form, such as in short fiber form, as well as fibers ofother materials which deposit on the walls of the casing and tubingstrings in admixture with the solid salt with or without a binder. Theconcentration of binder or filler is generated in the range of about 5to 20 weight percent of the salt in the solution.

Thus, according to the invention, there is provided a method ofinsulating a tubing string and a casing string in a well comprising thesteps of: setting a packer downhole on said tubing string to seal offthe annulus between the strings above a stratum penetrated by said well,substantially filling said annulus above said packer with a concentratedaqueous solution of a water-soluble inorganic salt; passing a hot fluidthru said tubing string so as to heat and boil said solution whileventing resulting steam from said annulus at the wellhead; andcontinuing the third step so as to evaporate said solution and depositsaid salt in solid form on the outside wall of said tubing string andthe inside wall of said casing string.

A more complete understanding of the invention may be had by referenceto the accompanying schematic drawing of which FIGURE 1 is an elevationin partial section thru an oil-bearing stratum penetrated by a well andFIG- URE 2 is an enlarged partial section of the insulated tubing andcasing of FIGURE 1.

Referring to the drawing, and particularly to FIGURE 1, a stratum 10containing oil is penetrated by a well 12 which is provided with acasing string 14 and a tubing string 16. Casing 14 is cemented at 18 andis perforated at 20. Valved conduit 22 connects with the annulus 24between the casing and tubing strings at the wellhead. A packer 26 sealsoff annulus 24 just above stratum 10. The inner wall of the casingstring is provided with a layer 28 of insulating material formed ofsolid inorganic salt including a binder and/or a filler. A similarinsulating layer 30 is provided on the outer wall of tubing string 16.

In applying the insulation to the tubing and. casing strings, theselected solution or slurry of salt with or without a binder and/ orfiller is injected thru conduit 22 into annulus 24 so as tosubstantially fill the annulus from packer 26 to the wellhead. Steam orother hot fluid is injected thru tubing string 16 and thru perforations20 into stratum 10 at such a rate as to raise the temperature of theaqueous solution in the annulus to its boiling temperature and evaporatewater therefrom, the same being vented thru conduit 22. As the level ofthe solution in annulus 24 is progressively lowered due to evaporation,solid salt is deposited on the outer wall of tubing string 16 and theinner wall of casing 14 to form substantial layers of insulatingmaterial on these strings. Even a inch or a /8 inch layer of porous salton the walls of the strings substantially reduces heat losses from theinjected steam during steam flooding of stratum 10 or, in the event thatwell 12 is a production well of a reverse in situ combustion operation,during venting of hot produced gases and vapors thru tubing string 16.However, it is feasible to deposit substantially thicker layers ofinsulating material on the walls of the annulus by the methd of theinvention. It is also feasible to substantially fill the annulus withwater-soluble insulating salt. The watersoluble nature of the insulatingmaterial facilitates the removal of the insulating material by passingwater thru the annulus at any time that it is desired to remove theinsulation. In order to do this, packer 26 may be released or unsealedso that flushing water may be injected down the tubing string and up theannulus to remove the insulating salt layer. It is also feasible tolower a water line or hose down the annulus substantially to packer 26and flush water up the annulus and out thru conduit 22 to dissolve andremove the salt layer.

To illustrate the invention, 400 grams of sodium carbonate were mixedwith 250 cc. of water, using an Osterizer on high speed for about tenminutes. This produced a viscous slurry of sodium carbonate in water. Asteel pipe nipple 4 inches long and inch ID. was cleaned by grinding offdirt and rust and one end thereof was plugged and the pipe was dippedinto the sodium carbonate slurry. The plug was removed from the end ofthe pipe and the pipe was clamped at a 45-degree angle on a ringstand.The pipe was then heated by directing a flame of an oxygen-natural gastorch thru the pipe for about five minutes. A substantial layer ofsodium carbonate insulation was produced on the outer surface of thepipe. It is quite obvious that a substantially heavier layer ofinsulating salt can be coated onto the pipe strings in the well byfilling the annulus with a concentrated aqueous solution of the salt andevaporating the water therefrom. Layers up to /8 inch in thickness andeven thicker layers can be produced by the method of the invention.

It is is desirable to clean the walls of the annulus to be coated withinsulating material by flushing with water or cleaning solution prior tothe filling of the annulus with the concentrated salt solution. Thisenhances the adherence of the salt to the wall of the iron pipe.

When producing the stratum with hot steam, the injected steam utilizedin evaporating the water from the annulus can be a part of the steaminjection operation, the steam and condensate from the injectionoperation passing from the Well below packer 26 directly into thestratum thru perforations 20.

It is also feasible to start a reverse burning in situ combustionprocess around well 12 with the annulus filled with salt solution andeffect the evaporation and deposition of salt with resulting hotproduced gases passing up the tubing string as the combustion iscontinued.

Certain modifications of the invention will become apparent to thoseskilled in the art and the illustrative details disclosed are not to beconstrued as imposing unnecessary limitations on the invention.

I claim:

1. A method of insulating a tubing string and a casing string in a wellcomprising the steps of:

(a) setting a packer downhole on said tubing string to seal off theannulus between the strings above a stratum penetrated by said well;

(b) substantially filling said annulus above said packer with aconcentrated aqueous solution of a water-soluble inorganic salt;

(c) passing a hot fluid thru said tubing string so as to heat and boilsaid solution while venting resulting steam from said annulus at thewellhead; and

(d) continuing step (c) so as to evaporate said solution and depositsaid salt in solid form on the outside wall of said tubing string andthe inside wall of said casing string.

2. The method of claim 1 wherein said inorganic salt is selected fromthe group consisting of borax, sodium carbonate, sodium sulfate, andmixtures thereof.

3. The method of claim 1 wherein a binder is incorporated in saidsolution.

4. The process of claim 1 wherein said hot fluid is steam being injectedinto said stratum in a steam drive oil production process.

References Cited UNITED STATES PATENTS 1,700,995 2/1929 Burns et al.138145 X 3,012,606 12/1961 Brooke l661 3,142,336 7/1964 Doscher 16657 X3,358,756 12/1967 Vogel 166-40 X 3,385,363 5/1968 Hamby et al 166-1 XOTHER REFERENCES Owens, W. D., et al.: Steam Stimulation for SecondaryRecovery. In Producers Monthly 29(4), April 1965, pp. 8 and 10-13.

CHARLES E. OCONNELL, Primary Examiner. I. A. CALVERT, AssistantExaminer.

U.S. Cl. X.R. 117-97; 16657

